In an electronic communication system, a transmitter may include an output amplifier, for example an amplifier apparatus, which raises the power of a transmission signal to an output level. The output level must be high enough to allow the transmission signal to be received by a receiver. In particular in a wireless communication system which is defined, for example, by one of the standards GSM (Global System for Mobile Communication), UMTS (Universal Mobile Telecommunication Standard) or W-CDMA (Wideband Code Division Multiple Access), the output level of a mobile terminal is predefined by a base station or according to a standardized specification.
In a time division multiplex method such as TDMA, the output level is switched according to a predefined time mask. In this case, a so-called isolation level of, for example, −36 dBm for GSM900 is first of all assumed. The output level is then raised or set to a target value (for example 5 dBm to 33 dBm for GSM900). Raising or setting the output level is also referred to as “ramping”.
The operation of setting the output level is often controlled by detecting a value of the output level using a power detector. This value can be compared with a target value in a control loop and the operation of setting the output level can be corrected in such a manner that a desired target value is assumed. Such a closed control loop is also referred to as a “closed loop” or “closed power loop”.
The problem in this case is that the bandwidth of the power level values which can possibly be assumed is generally wider than the bandwidth of known linear power detectors for measuring the output power. A closed control loop for monitoring the setting of an entire dynamic range of the transmitter therefore cannot be provided. Accordingly, the output power will usually be set with the aid of the closed control loop only in a section of the dynamic range. Sufficiently reliable control of the output power by way of the closed control loop will generally be expected for output powers of greater than 0 dBm.
Operations for controlling the output power which have a transition from an open operation of setting the output level, that is to say one which takes place without knowledge of the actual output level, a so-called “open loop” or “open power loop”, to the closed control loop or closed loop are therefore usually carried out.
In order to have a desired transition spectrum, a repeatable transition between the open loop and the closed loop may be required.